Process for blackening iron and steel and composition of matter therefor



Patented Dec. 25, 1951 OFFICE PROCESS FOR BLACKENING IRON AND STEEL AND COMPOSITION OF MATTER THEREFOR Isaac Laird Newell, Wethersfield, Conn.

No Drawing. Application March 11, 1950, Serial No. 149,204

Claims.

This invention relates toa process for blackening iron and steel and their alloys and a new composition of matter therefor. It has for its object the attainment of highly successful results in producing a black coating on such metal parts without the disadvantages attendant upon the use of baths heretofore used for this purpose.

Up to the present time, the art of blackening iron and steel and their alloys has been confined, for the most part, to processes which utilize nitrates and nitrites as oxidizing agents to give ferroso-ferric oxide film on the surface. These baths are highly caustic and must be operated at temperatures above 285 F. in order to produce satisfactory black surfaces. Due to the large amount of material necessary to maintain the bath at a boiling point. of above 285 F., the bath is viscous and loss of chemicals due to dragout is high.

Other methods of producing black films and finishes on steel also have disadvantages. A common method employs heating the iron or steel in an oxidizing salt bath or niter bath at temperatures of 750 to 1000 F. These temperatures often adversely afiect the strength and microstructure of the iron and steel parts.

I have discovered that a bath comprising an aqueous solution of a water soluble salt of an arylsulphonemonochlorarnide made alkaline with an alkali metal hydroxide such as sodium hydroxide is free from the objections mentioned above and is very effective in the blackening of iron and steel and their alloys. Of the arylsulphonemoncchloramides, I have found these having benzene or one of it's homologues as part of the molecule, to be especially suited for use in a ferrous metal blackening bath.

One compound of this group, particularly suitable from the standpoint of commercial use is the sodium salt of benzene-sulphonemonochlormide. This organic compound is not hazardous either in the dry state or solution from the standpoint of fires or explosion. Baths for the blackening of steel employing this material can vary widely in proportion and yet give a suitable black. As little as 0.5% by weight (of the whole solution) of the sulphcnemonochloramide together with sufficient sodium hydroxide to give a boiling point at 255 F. will produce an excellent blackening bath. Large amounts of the sulphonemonochlcramide will also give satisfactory baths for blackening of ferrous metals, but the solubility of the material is limited and the :excess sulphoneinonochloramide floats on the surface of the bath and tends to produce frothing. Moreover, there is no advantage from the standpoint of color or speed of the blackening from the use of high concentrations, andbecause of economy and better operation, I prefer the more dilute solutions.

Other alkalies than sodium hydroxide can be used satisfactorily in this blackening bath,'but the other alkalies such as potassium hydroxide and lithium hydroxide are not as effective as sodium hydroxide. I also prefer sodium hydroxide because of the lower cost of the sodium compound.

In Patent No. 2,475,981, dated July 12, 1949, I have disclosed a process for the blackening of copper and copper alloys which might use abath containing a solution of an aryl sulphone monochloramide and an alkali metal hydroxide. The process as therein disclosed with these ingredients is satisfactory for use at the temperatures stated in blackening copper metals but the same baths will not produce a blackening of ferrous metals. The present disclosure is directed to the use of these specific ingredients for the blackening of ferrous metals. There is a marked difference in the proportions of ingredients when used for the purposes of the present invention as will be apparent by comparison with this disclosure.

I have discovered, contrary to the usualpractice in the formulation of baths for the blackening of ferrous metals, that the relative amounts of the oxidizing agents in this case must be materially reduced in order to produce satisfactory reslts. It has long been thought essential for better results in ferrous blackening baths to increase the proportion of oxidizing agents. Furthermore, I have found that temperatures necessary in the use of the ingredients according to the present invention are materially lower than has been the experience with previous ferrous blackening baths. The temperatures of the pres ent invention may vary in therange of between 250 and 300 F.

Of the iron and steel alloys tested, I have found unusually good black coatings to be produced with pure iron and both low and high carbon steels. The lower alloy steels containing elements such as nickel, chromium, nickel-chromium, nickel chromium vanadium, nickelchromium-molybdenum, have also been given excellent black finishes. Even some of the stainless steels, such as the 12% chrome, are satisfactorily blackened by my process.

The following examples are set forth to illustrate the invention:

Example 1 Five grams by weight of the sodium salt of benzene sulphonemonochloramide, 100 grams sodium hydroxide and 200 grams of water were mixed and heated until boiling at a temperature of 255 F. It is usually necessary to boil the solution a short while in order to evaporate a small amount of the Water and raise the boiling point to 255 F. At this temperature (255 F.) a piece of steel containing 0.20% carbon was immersed in the bath for a period of five minutes. The steel sample was then removed from the bath and rinsed in water. A deep blue-black film was noted on the steel part, the film being found durable and tenacious.

I have found that blackening will occur on ferrous metals in such baths as have the hy droxide content at least 15 times the chloramide content. In working with proportions where the hydroxide is less than 15 times the chloramide, however, the bath commences to froth and difficulties of a physical nature are encountered at such lower ratios.

Example 2 One gram by weight of the sodium salt of toluene sulphone monochloramide and 125 grams of potassium hydroxide were ground together to make an intimate mixture. The mixture was added to 200 grams of water and heated to boiling. The boiling was continued until sufiicient evaporation of the water took place to have the boiling temperature raised to 290 F. A sample of pure iron wire immersed in this bath was colored with a blue black film which was tenacious and durable.

Example 3 A starting salt mixture was made by blending two grams of the sodium salt of benzene sulphone monochloramide with 100 grams of powered sodium hydroxide. Sufiicient water was added to give a boiling point of 265 F. and samples of steel wire were immersed in the bath with the following results:

Steel: Results #1010 carbon steel Good blue black #410 chrome stainless steel Good black 18-8 chrome-nickel stainless steel Brownish black 17% chrome steel Good black This bath was kept in good operation by the addition of a replenisher salt consisting of equal parts of sodium benzene-sulfonemonochloramide and sodium hydroxide.

What is claimed is:

1. A composition of matter for use in the blackening of iron and its alloys consisting of a mixture of an alkali metal salt of an aryl sulphone monochloramide made alkaline with an alkali metal hydroxide, the hydroxide content being at least fifteen times the weight of the monochloramide and not more than 125 times by weight of the monochloramide.

2. A composition of matter for use in the blackening of iron and its alloys consisting of a mixture of the sodium salt of an aryl sulphone monochloramide and an alkali metal hydroxide having the hydroxide content at least fifteen times by weight of the monochloramide and not more than 125 times by weight of the monochloramide.

3. A composition of matter for use in the blackening of iron and its alloys consisting of a mixture of the sodium salt of benzene sulphone monochloramide and sodium hydroxide, the sodium hydroxide content being at least fifteen times by weight of the monochloramide and not more than times by weight of the monochloramide.

4. A composition of matter for use in the blackening of iron and its alloys consisting of a 'mixture of the sodium salt of toluene sulphone monochloramide and sodium hydroxide, the sodium hydroxide content being at least fifteen times by weight of the monochloramide and not more than 125 times by weight of the monochloramide.

5. A composition of matter for use in the blackening of iron and its alloys consisting of a mixture of five parts by weight of the sodium salt of benzene sulphone monochloramide and one hundred parts by weight of sodium hydroxide.

6. The process of blackening iron and its alloys in which the metal is immersed in a solution consisting of a water solution of an alkali metal salt of an aryl sulphone monochloramide made alkaline with an alkali metal hydroxide, the hydroxide content being at least 15 times and not more than 125 times by weight of the chloramide, said solution containing sufficient water to give a boiling point from 250 to 300 F. and said solution being heated to a temperature between 250 and 300 F. and the metal held in said solution for a sufiicient time to produce the desired depth of black.

'7. The process of blackening iron and its alloys in which the metal is immersed in a solution consisting of a water solution of a sodium salt of an aryl sulphone monochloramide made alkaline with an alkali metal hydroxide, the hydroxide content being at least 15 times and not more than 125 times by weight of the chloramide, said solution containing sufiicient water to give a boiling point from 250 to 300 F. and said solution being heated to a temperature between 250 and 300 F. and the metal held in said solution for a sufiicient time to produce the desired depth of black.

8. The process of blackening iron and its alloys in which the metal is immersed in a solution consisting of a water solution of a sodium salt of benzene sulfone monochloramide made a1- kaline with an alkali metal hydroxide, the hydroxide content being at least 15 times and not more than 125 times by weight of the chloramide, said solution containing sufficient water to give a boiling point from 250 to 300 F. and said solution being heated to a temperature between 250 and 300 F. and the metal held in said solution for a sufficient time to produce the desired depth of black.

9. The process of blackening iron and its alloys in which the metal is immersed in a solution consisting of a water solution of a sodium salt of benzene sulfone monochloramide made alkaline with a sodium hydroxide, the hydroxide content being at least 15 times and not more than 125 times by weight of the chloramide, said solution containing sufiicient water to give a boiling point from 250 to 300 F. and said solution being heated to a temperature between 250 and 300 F. and the metal held in said solution for a sufficient time to produce the desired depth of black.

10. The process of blackening iron and its alloys in which the metal is immersed in a solution consisting of a water solution of a sodium salt of toluene sulphone monochloramide made alkaline with a sodium hydroxide, the hydroxide content being at least 15 times and not more 5 than 125 times by weight of the chloramide, said solution containing sufiicient water to give a boiling point from 250 to 300 F. and said solution being heated to a. temperature between 250 and 300 F. and the metal held in said solution for a sufiicient time to produce the desired depth of black.

ISAAC LAIRD NEWELL.

REFERENCES CITED The following references are of record in the file of this patent:

6 UNITED STATES PATENTS Number Number Name Date Bergstein Dec. 2, 1947 Newell July 12, 1949 FOREIGN PATENTS Country Date France Mar. 27, 1925 Switzerland Jan. 17, 1944 

6. THE PROCESS OF BLACKENING IRON AND ITS ALLOYS IN WHICH THE METAL IS IMMERSED IN A SOLUTION CONSISTING OF A WATER SOLUTION OF AN ALKALI METAL SALT OF AN ARYL SULPHONE MONOCHLORAMIDE MADE ALKALINE WITH AN ALKALI METAL HYDROXIDE, THE HYDROXIDE CONTENT BEING AT LEAST 15 TIMES AND NOT MORE THAN 125 TIMES BY WEIGHT OF HE CHLORAMIDE, SAID SOLUTION CONTAINING SUFFICIENT WATER TO GIVE A BOILING POINT FROM 250 TO 300* F. AND SAID SOLUTION BEING HEATED TO A TEMPERATURE BETWEEN 250 AND 300* F. AND THE METAL HELD IN SAID SOLUTION FOR A SUFFICIENT TIME TO PRODUCE THE DESIRED DEPTH OF BLACK. 